1. Field of the Invention
The invention concerns a device to absorb impact energy between the impacted component and a component to be protected from the effects of the impact, in particular between the bumper bracket and the frame side rail of a vehicle with a shock-absorbing part to plastically absorb energy located between the impacted component and the component to be protected from the effects of the impact and a shock-absorbing part to elastically absorb energy.
2. Description of Related Art
A device of the type to which the invention is directed particularly serves to protect the frame and body of vehicles from damage due to the impact energy arising from an impact.
The device operates in three basic stages depending on the impact speed of the vehicle:
1. Elastic energy absorption occurs at low speeds so that vehicles can drive away without damage after a corresponding collision. Depending on guidelines and corresponding regulations, the elastic absorption of energy occurs between 4 and 8 km/h.
2. At average speeds up to 15 km/h, the frame side rail should be protected to keep down damage that requires repairs. Within this speed range, the frame side rail remains undamaged and the energy is absorbed by plastic deformation.
3. At high speeds, the frame side rail should absorb energy by buckling or folding after plastic energy absorption. The frame side rails should retain their position particularly at the front of the vehicle to prevent on-sided bending.
It is prior art in steel embodiments to install a hydraulic part for elastic energy absorption inside a deforming cylinder for plastically absorbing energy. Since the deforming cylinder must have a small diameter to attain the necessary deformation force, the hydraulic part (if it is in the deforming cylinder) must also be small so that it can work under high pressure.
While such a design is possible with steel embodiments since steel alloys can be used with a yield point of approx. 1000 MPa in conjunction with wall thicknesses of 6 mm, an aluminum design is impossible since the permissible stress is, of course, lower than that for steel. Hence, the hydraulic part is not inside but must be located outside the deforming cylinder in aluminum embodiments.
Placing the impact absorber between the impacted component, in particular the bumper bracket, and the component to be protected from the impact (in particular the frame side rail) is not possible since large block lengths are created with such a design that prevent the optimum exploitation of the deformation path of stage 2 (plastic energy absorption). To be understood as xe2x80x9cblock lengthxe2x80x9d is the remaining component length of an energy absorbing element at which the level of force permissible for the use of the deformation path is exceeded. In extreme cases, the energy absorbing element acts rigid.
The problem on which the invention is based is therefore to design a device of the initially mentioned type so that it can be constructed out of aluminum without creating large block lengths.
This problem is solved according to the invention by placing the elastic energy absorbing part before the plastic energy absorbing part (viewed in direction of impact) inside the component that is to be protected from the effects of the impact energy.
This design makes it possible to use a hydraulic element with a large plunger diameter that operates with low hydraulic-fluid pressure. The required permissible stress and wall thickness of the fluid and gas cylinders of the hydraulic element are lower.
In the following, a particularly preferred exemplary embodiment of the invention will be further described with reference to the accompanying drawings.